Generally in the prior art, well bore packing devices, commonly known as cast-iron bridge plugs/packers, use one-piece slip assemblies as a means to anchor the packing device to the tubular member of the well to be sealed off. The slip assembly is critical to the success of the packing device anchoring in place and maintaining well control. Various problems are encountered with the prior art in deployment of prior art slips, some of which may lead to a failure of the packer to anchor and seal.
Prior art slips may have a tapered inner diameter. There is usually a series of cuts or reduced wall thickness areas evenly spaced around the circumference of the slip assembly to predispose the slip assembly to fracture into multiple segments when compressed against the mating inner diameter taper of a cone run congruent to the slip on the center mandrel of the tool assembly.
As those of ordinary skill in the art will recognize, a potential problem with the prior art arrangement is that not all segments must fracture for the slip to deploy and there is no assurance that any symmetrical spacing around the circumference of the packing device is maintained. This can lead to the packing device being slightly offset from the centerline of the tubular member to be sealed off. The compression of the slip against the cone causes the slip to separate into pieces and wedge between the cone and the inner diameter of the tubular member. If the slip assembly is not anchored in any way to the cone or to the body of the plug assembly, the slip segments are subject to non-aligned irregular contact against the inner diameter of the tubular member (e.g. a slip segment may rotate off axis with the tubular).
This problem is made worse in the actual setting dynamic by the sudden movement (relief) that takes place when the slip which is subjected to the force required to break the segments is no longer retained on the plug mandrel, in a sense, the slip segments accelerate away from the mandrel independent of the movement of the cone. This restricts the plug to being used in a tubular member with an inner diameter close to the diameter of the plug. As the annular space increases between the plug and the tubular inner diameter, the potential for irregular slip deployment is higher. Thus, this problem prevents the one piece segmented assembly from being used in applications with high expansion ratio over the original diameter of the un-segmented slip.
In the setting operation of the prior art slips, the upper set of slips normally sets first and the slips on the lower (or opposite) end then deploy and are dragged up the inner diameter of the pipe in which the plug is being set during the final compression of the elastomer. This creates friction/drag that must be overcome by force from the setting tool. The setting tool releases the plug when a predetermined force is achieved. Excessive drag may cause release of the plug from the setting tool before optimum compression of the elastomer is achieved thus possibly reducing the effectiveness of the elastomer seal.
Therefore, the present invention solves these problems associated with the prior art. An object of the disclosed apparatus and method is that the slips deploy in a relatively even manner around the circumference of the well packing device. Another object of the present disclosure is that the device controls the timing of deployment thereby controlling the load transfer into the packing element during deployment. Yet another object is that the present apparatus controls the setting range in which the slips can function properly. Still yet another object is that the present disclosure allows for a higher deployment diameter for slip extension when compared to prior art packers.